This disclosure relate to an image forming apparatus using an electrophotographic system in particular, such as a copier, a printer, a facsimile, or a multifunction peripheral combining them together and a developing device of such an image forming apparatus, and to a technology of detecting concentration of a toner used in the developing device.
In the image forming apparatus such as the multifunction peripheral, a developing device is provided to attach a toner to an electrostatic latent image formed on a surface of a photoconductive drum to develop the electrostatic latent image. For example, as developer used in the developing device, binary-type developer composed of a toner and magnetic carriers is widely used. In such a device, a blend ratio between the toner and the carriers (toner concentration) is a significant factor in terms of effects of development. That is, when the toner concentration becomes equal to or less than an appropriate value, image concentration decreases, and when the toner concentration becomes equal to or more than the appropriate value, a problem such as so-called fogging occurs.
Therefore, to obtain a favorable image by the image forming apparatus, it is required to accurately detect the toner concentration and control the toner concentration at the appropriate value. As configuration for the toner concentration detection, for example, a magnetic detector detecting a change in magnetic permeability in developer or an optical detector detecting reflective light of developer is used. The concentration detector normally has a detection surface of a detection section on an inner surface of a container having a toner refill port, but toner adherence to the detection surface of the detection section results in failure to perform accurate detection, causing an error.
Thus, a developing device has already been suggested which having a blade provided on an inner surface of the container to clean the detection surface. In this device, a stirring plate is fixed to a stirring member which stirs developer while making rotation, and this stirring plate is arranged at a position opposing a detection surface of a toner concentration sensor. Fixed on a one-side surface of this stirring plate is a flexible blade. A length of the blade is set at a length which permits a tip of the blade to reach the detection surface. In this device, deflection of the blade is utilized to perform cleaning of the detection surface.